1. Field of the Invention
This invention relates to capacitive voltammetry, and more specifically to capacitive voltametric measurements involving the application of relatively large time-varying electric fields to low-permitivity non-aqueous liquid suspensions of charged particles.
2. Description of the Prior Art
Non-aqueous suspensions of charged particles are employed in many diverse art areas, such as paints, cosmetics, ceramics, and electrostatic toners for copying machines.
Examples of such suspensions include:
(1) Oxides, carbides, and nitrides of such materials as aluminum, berylium, titanium, zirconium, silicon and boron suspended in non-aqueous media for use in fabrication of electronic materials. These materials include substrates, IC packages, insulators, capacitors, thermistors, varisitors, and other materials for the electronics industry;
(2) Liquid electrostatic toners which consist of pigment dispersions in non-aqueous liquid;
(3) Suspensions of iron oxides to produce magnetic recording disks; and
(4) Dispersions of pesticides.
These are distinct from other chemical compositions in that:
(a) these materials consist of a dispersion of particles suspended in a liquid; and
(b) the particles are charged, usually by addition of a surfactant, either to control deposition or to enhance stability of the dispersion.
An elementary form of voltammetry has been employed and marketed by the Indigo Company, Rehovot, Israel in an effort to characterize properties of electrostatic toner suspensions. That company's CHARGEMETER with PCI Data Acquisition System instrument applies a step voltage to two capacitive electrodes having a sample of toner displaced therebetween. The resulting transient current versus time waveform is recorded, and correlations are made with standardized data in order to draw certain conclusions about characteristics of the toner. Typical test waveforms thereof are shown in FIG. 1. Based on the height, width, and time displacement transient waveform, an operator can obtain useful approximate values for charge to mass ratio of the sample and conductivity of the sample at the applied voltage. That approach is somewhat useful, but it is limited in that the contributions to the current from the particles and the surrounding solution cannot easily be separated and the response of the materials as a function of frequency of the applied voltage cannot be determined.
It is therefore an object of the instant invention to provide an improved measurement technique that will result in more complete and accurate characterizations of nonaqueous liquid suspensions of charged particles.
It is another object of this invention to use the test results obtained to accomplish monitoring and automatic control of machinery and processes that employ non-aqueous liquid suspensions of charged particles.
These and other objects of the invention will become more clear to the reader upon careful perusal of the following Summary, Drawing, Detailed Description and appended Claims.